1. Field of the Invention
This invention relates to an improved multi-disc friction brake which includes a basic actuation piston and bore configuration which is simple and less expensive to provide and, more specifically, to such a brake which is improved to include a parking brake feature while utilizing many of the identical parts of a basic brake without the parking brake feature.
2. Description of the Prior Art
There have heretofore been utilized a number of friction brakes which employ a plurality of relatively rotating friction discs and a means for applying compressive forces therebetween to produce the braking action. Some such friction brakes as those disclosed in U.S. Pat. Nos. 3,927,737; 3,941,219; and 4,146,116, utilize a circular actuation piston which has a cross-section at one side thereof which is generally L-shaped. Other brake configurations, such as those disclosed in U.S. Pat. Nos. 3,132,724 and 3,198,295, use a circular piston which is generally annular. Still other friction brakes, such as those disclosed in U.S. Pat. Nos. 3,081,842; 3,301,359; and 4,173,269, employ actuation pistons which have at one side thereof a generally T-shaped cross-section.
While the actuation piston devices in each of these friction brakes include a number of features which are quite different, there has remained a common problem of manufacturing tolerances and general engineering manufacturing instructions in the formation of each which contributes significantly to the overall expense and complexity of manufacturing these brakes. In general, their manufacture included a common concern for the tolerances of various diameters, the tolerances regarding concentricity of various surfaces, the smoothness of various surfaces during final machining and the tolerances and dimensions of piston or seal ring grooves formed in the surfaces.
A basic brake for use in the heavy duty vehicle field, as disclosed in a co-pending application by the same inventor, U.S. Ser. No. 193,511 filed on Oct. 2, 1980, and entitled "Friction Brake," has been designed to eliminate some of these problems and concerns. However, different vehicles have different brake requirements. In some installations the basic brake can be satisfactorily employed while the brake for other installations must include a parking brake feature. It has not been uncommon in the past to provide two completely different brakes for these installations. If the brakes utilize completely different parts, tooling and inventory requirements are increased and assembly and maintenance procedures are more complicated.